Based on its effect on soil pH, gypsum is neither an acid nor a base.
Understanding Gypsum and Soil pH
The provided reference clearly states that gypsum "will not change the soil pH". This is the key characteristic that determines its classification in terms of acidity or basicity in the context of soil science and agriculture.
- An acid lowers pH.
- A base (or alkali) raises pH.
Since gypsum has no significant impact on soil pH levels, it cannot be classified as either an acid or a base. Its chemical formula is CaSO₄·2H₂O (calcium sulfate dihydrate), and when dissolved in water, it dissociates into calcium ions (Ca²⁺) and sulfate ions (SO₄²⁻). These ions typically do not participate in reactions that significantly alter the concentration of hydrogen ions (H⁺) or hydroxide ions (OH⁻) in the soil solution, which are the primary drivers of pH changes.
What Gypsum Does Do
While gypsum doesn't act as an acid or a base to change pH, it provides several other benefits as a soil amendment:
- Does not change soil pH: Crucially, it maintains the existing pH level.
- Not acid soluble: (As stated in the reference) This further underscores its stability and lack of acidic properties.
- Shifts Ca and Mg levels: It is a source of calcium, which can influence the balance of other cations like magnesium in the soil structure and solution.
- Provides sulfate sulfur: It offers a readily available form of sulfate sulfur, an essential secondary nutrient for plant growth and soil health.
These properties make gypsum a valuable tool for improving soil structure (e.g., breaking up compacted clay soils) and supplying nutrients without altering the soil's pH, which is particularly useful in soils that already have the desired acidity or alkalinity.
For more information on soil amendments, you can consult resources like university extension offices or agricultural science websites.
Key Takeaways
| Property Related to pH | Gypsum's Effect | Classification (in soil context) |
|---|---|---|
| Ability to lower pH | None | Not an acid |
| Ability to raise pH | None | Not a base |
| Overall pH Impact | Will not change pH | Neutral |
In summary, gypsum is primarily used for its calcium and sulfur content and its ability to improve soil physical properties, not for adjusting soil pH.
